Determining rounding offset using scaling factor in picture resampling

ABSTRACT

An apparatus for coding video information according to certain aspects includes a memory and a processor. The memory unit is configured to store video information associated with a reference layer picture and an enhancement layer picture. The processor is configured to: store video information associated with a reference layer picture and an enhancement layer picture; receive a scale factor that indicates a proportion of scaling between the reference layer picture and the enhancement layer picture in a first direction; determine, without performing a division operation, a rounding offset value using the scale factor; and determine a coordinate in the first direction of a first sample located in the reference layer picture that corresponds to a second sample located in the enhancement layer picture using the scale factor and the rounding offset value.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/829,926, filed May 31, 2013, which is incorporated by reference inits entirety.

BACKGROUND

Field

This disclosure is related to the field of video coding and compression.In particular, it is related to scalable video coding (SVC), includingSVC for Advanced Video Coding (AVC), as well as SVC for High EfficiencyVideo Coding (HEVC), which is also referred to as Scalable HEVC (SHVC).It is also related to 3D video coding, such as the multiview extensionof HEVC, referred to as MV-HEVC. Various embodiments relate to systemsand methods for determining rounding offsets used in resampling process.

Description of the Related Art

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard presentlyunder development, and extensions of such standards. The video devicesmay transmit, receive, encode, decode, and/or store digital videoinformation more efficiently by implementing such video codingtechniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame or a portion of a video frame) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to a referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy coding maybe applied to achieve even more compression.

SUMMARY

In general, this disclosure describes techniques related to scalablevideo coding (SVC). Various techniques described below provide methodsand devices for determining rounding offsets used in resampling process.

An apparatus for coding video information according to certain aspectsincludes a memory and a processor. The memory unit is configured tostore video information associated with a reference layer picture and anenhancement layer picture. The processor is configured to: store videoinformation associated with a reference layer picture and an enhancementlayer picture; receive a scale factor that indicates a proportion ofscaling between the reference layer picture and the enhancement layerpicture in a first direction; determine, without performing a divisionoperation, a rounding offset value using the scale factor; and determinea coordinate in the first direction of a first sample located in thereference layer picture that corresponds to a second sample located inthe enhancement layer picture using the scale factor and the roundingoffset value.

The details of one or more examples are set forth in the accompanyingdrawings and the description below, which are not intended to limit thefull scope of the inventive concepts described herein. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the drawings, reference numbers may be re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate example embodiments described herein and are not intended tolimit the scope of the disclosure.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 2B is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3B is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 4 is a block diagram illustrating an example of determiningrounding offsets used in resampling process, according to aspects of thedisclosure.

FIG. 5 is a flowchart illustrating one embodiment of a method fordetermining rounding offsets used in resampling process, according toaspects of this disclosure.

FIG. 6 is a flowchart illustrating another embodiment of the method fordetermining rounding offsets used in resampling process, according toaspects of this disclosure.

DETAILED DESCRIPTION

The techniques described in this disclosure generally relate to scalablevideo coding (SHVC, SVC) and multiview/3D video coding (e.g., multiviewcoding plus depth, MVC+D). For example, the techniques may be relatedto, and used with or within, a High Efficiency Video Coding (HEVC)scalable video coding (SVC, sometimes referred to as SHVC) extension. Inan SHVC, SVC extension, there could be multiple layers of videoinformation. The layer at the very bottom level may serve as a baselayer (BL), and the layer at the very top (or the highest layer) mayserve as an enhanced layer (EL). The “enhanced layer” is sometimesreferred to as an “enhancement layer,” and these terms may be usedinterchangeably. The base layer is sometimes referred to as a “referencelayer,” (RL) and these terms may also be used interchangeably. Alllayers in between the base layer and the top layer may serve as eitheror both ELs or reference layers (RLs). For example, a layer in themiddle may be an EL for the layers below it, such as the base layer orany intervening enhancement layers, and at the same time serve as a RLfor the enhancement layers above it. Each layer in between the baselayer and the top layer (or the highest layer) is may be used as areference for inter-layer prediction by a higher layer and may use alower layer as a reference for inter-layer prediction.

For simplicity, examples are presented in terms of just two layers: a BLand an EL; however, it should be well understood that the ideas andembodiments described below are applicable to cases with multiplelayers, as well. In addition, for ease of explanation, the terms“frames” or “blocks” are often used. However, these terms are not meantto be limiting. For example, the techniques described below can be usedwith any of a variety of video units, including but not limited topixels, blocks (e.g., CU, PU, TU, macroblocks, etc.), slices, frames,picture, etc.

Video Coding

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multi-view Video Coding (MVC) and Multi-viewCoding plus Depth (MVC+D) extensions. The latest HEVC draftspecification, and referred to as HEVC WD10 hereinafter, is availablefromhttp://phenix.int-evey.fr/jct/doc_end_user/documents/12_Geneva/wg11/JCTVC-L1003-v34.zip.The multiview extension to HEVC, namely MV-HEVC, is also being developedby the JCT-3V. A recent Working Draft (WD) of MV-HEVC WD3 hereinafter,is available fromhttp://phenix.it-sudparis.eu/jct2/doc_end_user/documents/3_Geneva/wg11/JCT3V-C1004-v4.zip.The scalable extension to HEVC, named SHVC, is also being developed bythe JCT-VC. A recent Working Draft (WD) of SHVC and referred to as SHVCWD2 hereinafter, is available fromhttp://phenix.int-evry.fr/jct/doc_end_user/documents/13_Incheon/wg11/JCTVC-M1008-v1.zip.

In SVC, SHVC, video information may be provided as multiple layers. Thelayer at the very bottom level can just serve as a base layer (BL) andthe layer at the very top level can serve as an enhancement layer (EL).All the layers between the top and bottom layers may serve as bothenhancement layers and base layers. For example, a layer in the middlecan be an EL for the layers below it, and at the same time as a BL forthe layers above it. For simplicity of description, we can assume thatthere are two layers, a BL and an EL, in illustrating the techniquesdescribed below. However, all the techniques described herein areapplicable to cases with multiple (more than two) layers, as well.

Scalable video coding (SVC) may be used to provide quality (alsoreferred to as signal-to-noise (SNR)) scalability, spatial scalabilityand/or temporal scalability. For example, in one embodiment, a referencelayer (e.g., a base layer) includes video information sufficient todisplay a video at a first quality level and the enhancement layerincludes additional video information relative to the reference layersuch that the reference layer and the enhancement layer together includevideo information sufficient to display the video at a second qualitylevel higher than the first level (e.g., less noise, greater resolution,better frame rate, etc.). An enhanced layer may have different spatialresolution than a base layer. For example, the spatial aspect ratiobetween EL and BL can be 1.0, 1.5, 2.0 or other different ratios invertical and horizontal directions. In other words, the spatial aspectof the EL may equal 1.0, 1.5, or 2.0 times the spatial aspect of the BL.In some examples, the scaling factor of the EL may be greater than theBL. For example, a size of pictures in the EL may be greater than a sizeof pictures in the BL. In this way, it may be possible, although not alimitation, that the spatial resolution of the EL is larger than thespatial resolution of the BL.

In SVC, which refers to the SVC extension for H.264 or the SHVCextension for H.265 (as discussed above), prediction of a current blockmay be performed using the different layers that are provided for SVC.Such prediction may be referred to as inter-layer prediction.Inter-layer prediction methods may be utilized in SVC in order to reduceinter-layer redundancy. Some examples of inter-layer prediction mayinclude inter-layer intra prediction, inter-layer motion prediction, andinter-layer residual prediction. Inter-layer intra prediction uses thereconstruction of co-located blocks in the base layer to predict thecurrent block in the enhancement layer. Inter-layer motion predictionuses motion information (including motion vectors) of the base layer topredict motion in the enhancement layer. Inter-layer residual predictionuses the residue of the base layer to predict the residue of theenhancement layer.

Overview

In SHVC, if a reference layer picture size is different from theenhancement layer picture size, a resampling (or upsampling) process canbe applied to the reference layer picture to match the size of theenhancement layer picture for inter-layer prediction. To resample thereference layer picture, an N tap resampling filter can be applied foreach color component. In the filtering process, the sample (or pixel)magnitudes of the reference layer picture can be multiplied by filtercoefficients and summed up. Since the size of the reference layerpicture and the size of the enhancement layer picture are different, thecoordinates of the reference layer samples involved in the filteringprocess may be defined. For example, the sample location of thereference layer picture that corresponds to the sample location of thecurrent enhancement layer picture can be determined so that sample(s)indicated by the sample location of the reference layer picture can beused in the resampling process.

During resampling process, an additional rounding offset can be applied.Rounding offsets can be added in determining the sample location of thereference layer picture to be resampled. For example, an additionalrounding offset addY can be applied in the vertical direction.Similarly, an additional rounding offset addX can be applied in thehorizontal direction. The sample location of the reference layer picturecan be defined by a horizontal sample location and a vertical samplelocation. The horizontal rounding offset can be added in determining thehorizontal sample location of the reference layer picture forresampling, and the vertical rounding offset can be added in determiningthe vertical sample location of the reference layer picture forresampling.

In the Working Draft 2 of SHVC, addY is calculated as follows:addY=(((RefLayerPicHeightInSamplesL*phaseY)<<14)+(ScaledRefLayerPicHeightInSamplesL>>1))/ScaledRefLayerPicHeightInSamplesL,where RefLayerPicHeightInSamplesL indicates the height of the referencelayer picture and ScaledRefLayerPicHeightInSamplesL indicates the heightof the scaled or resampled reference layer picture. However, using adivision operation to calculate addY can be expensive. Accordingly, itwould be advantageous to calculate addY in a more efficient manner.

In order to address these and other challenges, the techniques describedin this disclosure can calculate the rounding offsets used in resamplingof the reference layer picture without performing a division operationby using the previously calculated scaling factors. The scaling factorscan include a horizontal scaling factor ScaleFactorX and a verticalscaling factor ScaleFactorY. The horizontal scaling factor and thevertical scaling factor may also be referred to as the horizontal scalefactor and the vertical scale factor, respectively. The horizontalscaling factor and the vertical scaling factor may indicate theproportion of scaling between the reference layer picture and theenhancement layer picture in the horizontal direction and the proportionof scaling between the reference layer picture and the enhancement layerpicture in the vertical direction, respectively. ScaleFactorX andScaleFactorY may be calculated as follows:ScaleFactorX=((RefLayerPicWidthInSamplesL<<16)+(ScaledRefLayerPicWidthInSamplesL>>1))/ScaledRefLayerPicWidthInSamplesLScaleFactorY=((RefLayerPicHeightInSamplesL<<16)+(ScaledRefLayerPicHeightInSamplesL>>1))/ScaledRefLayerPicHeightInSamplesL,where RefLayerPicWidthInSamplesL and RefLayerPicHeightInSamplesLindicate the width and the height of the reference layer picture,respectively, and ScaledRefLayerPicWidthInSamplesL andScaledRefLayerPicHeightInSamplesL indicate the width and the height ofthe scaled or resampled reference layer picture, respectively.

Since the calculation for the scaling factors is similar to calculationfor the rounding offsets, the techniques can utilize the scaling factorsin calculating the rounding offsets. As explained above, there can be arounding offset for the horizontal direction and a rounding offset forthe vertical direction. In one embodiment, addY and addX can becalculated as follows:addY=(ScaleFactorY*phaseY+offset)>>2,addX=(ScaleFactorX*phaseX+offset)>>2,wherein offset can be some number (e.g., 0, 1, 2, etc.).

Generally, the scaling factors are available when the rounding offsetsare calculated, and therefore, the rounding offsets can be calculatedbased on the scaling factors without performing a division operation.Since a division operation is expensive, the rounding offsets can becalculated more efficiently by eliminating a division operation. As aresult, the coding process can be performed more efficiently as well.

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the invention. For example, an apparatus may be implemented or amethod may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

Video Coding System

FIG. 1 is a block diagram that illustrates an example video codingsystem 10 that may utilize techniques in accordance with aspectsdescribed in this disclosure. As used described herein, the term “videocoder” refers generically to both video encoders and video decoders. Inthis disclosure, the terms “video coding” or “coding” may refergenerically to video encoding and video decoding.

As shown in FIG. 1, video coding system 10 includes a source device 12and a destination device 14. Source device 12 generates encoded videodata. Destination device 14 may decode the encoded video data generatedby source device 12. Source device 12 can provide the video data to thedestination device 14 via a communication channel 16, which may includea computer-readable storage medium or other communication channel.Source device 12 and destination device 14 may include a wide range ofdevices, including desktop computers, notebook (e.g., laptop) computers,tablet computers, set-top boxes, telephone handsets, such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, displaydevices, digital media players, video gaming consoles, in-car computers,video streaming devices, or the like. Source device 12 and destinationdevice 14 may be equipped for wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia communication channel 16. Communication channel 16 may comprise atype of medium or device capable of moving the encoded video data fromsource device 12 to destination device 14. For example, communicationchannel 16 may comprise a communication medium to enable source device12 to transmit encoded video data directly to destination device 14 inreal-time. The encoded video data may be modulated according to acommunication standard, such as a wireless communication protocol, andtransmitted to destination device 14. The communication medium maycomprise a wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network, such asthe Internet. The communication medium may include routers, switches,base stations, or other equipment that may be useful to facilitatecommunication from source device 12 to destination device 14.

In some embodiments, encoded data may be output from output interface 22to a storage device. In such examples, channel 16 may correspond to astorage device or computer-readable storage medium that stores theencoded video data generated by source device 12. For example,destination device 14 may access the computer-readable storage mediumvia disk access or card access. Similarly, encoded data may be accessedfrom the computer-readable storage medium by input interface 28. Thecomputer-readable storage medium may include any of a variety ofdistributed or locally accessed data storage media such as a hard drive,Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatilememory, or other digital storage media for storing video data. Thecomputer-readable storage medium may correspond to a file server oranother intermediate storage device that may store the encoded videogenerated by source device 12. Destination device 14 may access storedvideo data from the computer-readable storage medium via streaming ordownload. The file server may be a type of server capable of storingencoded video data and transmitting that encoded video data to thedestination device 14. Example file servers include a web server (e.g.,for a website), an FTP server, network attached storage (NAS) devices,or a local disk drive. Destination device 14 may access the encodedvideo data through a standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thecomputer-readable storage medium may be a streaming transmission, adownload transmission, or a combination of both.

The techniques of this disclosure can apply applications or settings inaddition to wireless applications or settings. The techniques may beapplied to video coding in support of a of a variety of multimediaapplications, such as over-the-air television broadcasts, cabletelevision transmissions, satellite television transmissions, Internetstreaming video transmissions, such as dynamic adaptive streaming overHTTP (DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some embodiments, system 10 may be configured tosupport one-way or two-way video transmission to support applicationssuch as video streaming, video playback, video broadcasting, and/orvideo telephony.

In FIG. 1, source device 12 includes video source 18, video encoder 20,and output interface 22. Destination device 14 includes input interface28, video decoder 30, and display device 32. Video encoder 20 of sourcedevice 12 may be configured to apply the techniques for coding abitstream including video data conforming to multiple standards orstandard extensions. In other embodiments, a source device and adestination device may include other components or arrangements. Forexample, source device 12 may receive video data from an external videosource 18, such as an external camera. Likewise, destination device 14may interface with an external display device, rather than including anintegrated display device.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. Video source 18 may generate computer graphics-baseddata as the source video, or a combination of live video, archivedvideo, and computer-generated video. In some embodiments, if videosource 18 is a video camera, source device 12 and destination device 14may form so-called camera phones or video phones. The captured,pre-captured, or computer-generated video may be encoded by videoencoder 20. The encoded video information may be output by outputinterface 22 to a communication channel 16, which may include acomputer-readable storage medium, as discussed above.

Computer-readable storage medium may include transient media, such as awireless broadcast or wired network transmission, or storage media(e.g., non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. A network server (not shown) may receiveencoded video data from source device 12 and provide the encoded videodata to destination device 14 (e.g., via network transmission). Acomputing device of a medium production facility, such as a discstamping facility, may receive encoded video data from source device 12and produce a disc containing the encoded video data. Therefore,communication channel 16 may be understood to include one or morecomputer-readable storage media of various forms.

Input interface 28 of destination device 14 can receive information fromcommunication channel 16. The information of communication channel 16may include syntax information defined by video encoder 20, which can beused by video decoder 30, that includes syntax elements that describecharacteristics and/or processing of blocks and other coded units, e.g.,GOPs. Display device 32 displays the decoded video data to a user, andmay include any of a variety of display devices such as a cathode raytube (CRT), a liquid crystal display (LCD), a plasma display, an organiclight emitting diode (OLED) display, or another type of display device.

Video encoder 20 and video decoder 30 may operate according to a videocoding standard, such as the High Efficiency Video Coding (HEVC)standard presently under development, and may conform to the HEVC TestModel (HM). Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard. Other examples of video coding standardsinclude MPEG-2 and ITU-T H.263. Although not shown in FIG. 1, in someaspects, video encoder 20 and video decoder 30 may each be integratedwith an audio encoder and decoder, and may include appropriate MUX-DEMUXunits, or other hardware and software, to handle encoding of both audioand video in a common data stream or separate data streams. Ifapplicable, MUX-DEMUX units may conform to the ITU H.223 multiplexerprotocol, or other protocols such as the user datagram protocol (UDP).

FIG. 1 is merely an example and the techniques of this disclosure mayapply to video coding settings (e.g., video encoding or video decoding)that do not necessarily include any data communication between theencoding and decoding devices. In other examples, data can be retrievedfrom a local memory, streamed over a network, or the like. An encodingdevice may encode and store data to memory, and/or a decoding device mayretrieve and decode data from memory. In many examples, the encoding anddecoding is performed by devices that do not communicate with oneanother, but simply encode data to memory and/or retrieve and decodedata from memory.

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a non-transitorycomputer-readable medium and execute the instructions in hardware usingone or more processors to perform the techniques of this disclosure.Each of video encoder 20 and video decoder 30 may be included in one ormore encoders or decoders, either of which may be integrated as part ofa combined encoder/decoder (CODEC) in a respective device. A deviceincluding video encoder 20 and/or video decoder 30 may comprise anintegrated circuit, a microprocessor, and/or a wireless communicationdevice, such as a cellular telephone.

The JCT-VC is working on development of the HEVC standard. The HEVCstandardization efforts are based on an evolving model of a video codingdevice referred to as the HEVC Test Model (HM). The HM presumes severaladditional capabilities of video coding devices relative to existingdevices according to, e.g., ITU-T H.264/AVC. For example, whereas H.264provides nine intra-prediction encoding modes, the HM may provide asmany as thirty-three intra-prediction encoding modes.

In general, the working model of the HM describes that a video frame orpicture may be divided into a sequence of treeblocks or largest codingunits (LCU) that include both luma and chroma samples. Syntax datawithin a bitstream may define a size for the LCU, which is a largestcoding unit in terms of the number of pixels. A slice includes a numberof consecutive treeblocks in coding order. A video frame or picture maybe partitioned into one or more slices. Each treeblock may be split intocoding units (CUs) according to a quadtree. In general, a quadtree datastructure includes one node per CU, with a root node corresponding tothe treeblock. If a CU is split into four sub-CUs, the nodecorresponding to the CU includes four leaf nodes, each of whichcorresponds to one of the sub-CUs.

Each node of the quadtree data structure may provide syntax data for thecorresponding CU. For example, a node in the quadtree may include asplit flag, indicating whether the CU corresponding to the node is splitinto sub-CUs. Syntax elements for a CU may be defined recursively, andmay depend on whether the CU is split into sub-CUs. If a CU is not splitfurther, it is referred as a leaf-CU. In this disclosure, four sub-CUsof a leaf-CU will also be referred to as leaf-CUs even if there is noexplicit splitting of the original leaf-CU. For example, if a CU at16×16 size is not split further, the four 8×8 sub-CUs will also bereferred to as leaf-CUs although the 16×16 CU was never split.

A CU has a similar purpose as a macroblock of the H.264 standard, exceptthat a CU does not have a size distinction. For example, a treeblock maybe split into four child nodes (also referred to as sub-CUs), and eachchild node may in turn be a parent node and be split into another fourchild nodes. A final, unsplit child node, referred to as a leaf node ofthe quadtree, comprises a coding node, also referred to as a leaf-CU.Syntax data associated with a coded bitstream may define a maximumnumber of times a treeblock may be split, referred to as a maximum CUdepth, and may also define a minimum size of the coding nodes.Accordingly, a bitstream may also define a smallest coding unit (SCU).This disclosure uses the term “block” to refer to any of a CU, PU, orTU, in the context of HEVC, or similar data structures in the context ofother standards (e.g., macroblocks and sub-blocks thereof in H.264/AVC).

A CU includes a coding node and prediction units (PUs) and transformunits (TUs) associated with the coding node. A size of the CUcorresponds to a size of the coding node and must be square in shape.The size of the CU may range from 8×8 pixels up to the size of thetreeblock with a maximum of 64×64 pixels or greater. Each CU may containone or more PUs and one or more TUs. Syntax data associated with a CUmay describe, for example, partitioning of the CU into one or more PUs.Partitioning modes may differ between whether the CU is skip or directmode encoded, intra-prediction mode encoded, or inter-prediction modeencoded. PUs may be partitioned to be non-square in shape. Syntax dataassociated with a CU may also describe, for example, partitioning of theCU into one or more TUs according to a quadtree. A TU can be square ornon-square (e.g., rectangular) in shape.

The HEVC standard allows for transformations according to TUs, which maybe different for different CUs. The TUs are typically sized based on thesize of PUs within a given CU defined for a partitioned LCU, althoughthis may not always be the case. The TUs are typically the same size orsmaller than the PUs. In some examples, residual samples correspondingto a CU may be subdivided into smaller units using a quadtree structureknown as “residual quad tree” (RQT). The leaf nodes of the RQT may bereferred to as transform units (TUs). Pixel difference values associatedwith the TUs may be transformed to produce transform coefficients, whichmay be quantized.

A leaf-CU may include one or more prediction units (PUs). In general, aPU represents a spatial area corresponding to all or a portion of thecorresponding CU, and may include data for retrieving a reference samplefor the PU. Moreover, a PU includes data related to prediction. Forexample, when the PU is intra-mode encoded, data for the PU may beincluded in a residual quadtree (RQT), which may include data describingan intra-prediction mode for a TU corresponding to the PU. As anotherexample, when the PU is inter-mode encoded, the PU may include datadefining one or more motion vectors for the PU. The data defining themotion vector for a PU may describe, for example, a horizontal componentof the motion vector, a vertical component of the motion vector, aresolution for the motion vector (e.g., one-quarter pixel precision orone-eighth pixel precision), a reference picture to which the motionvector points, and/or a reference picture list (e.g., List 0, List 1, orList C) for the motion vector.

A leaf-CU having one or more PUs may also include one or more transformunits (TUs). The transform units may be specified using an RQT (alsoreferred to as a TU quadtree structure), as discussed above. Forexample, a split flag may indicate whether a leaf-CU is split into fourtransform units. Then, each transform unit may be split further intofurther sub-TUs. When a TU is not split further, it may be referred toas a leaf-TU. Generally, for intra coding, all the leaf-TUs belonging toa leaf-CU share the same intra prediction mode. That is, the sameintra-prediction mode is generally applied to calculate predicted valuesfor all TUs of a leaf-CU. For intra coding, a video encoder maycalculate a residual value for each leaf-TU using the intra predictionmode, as a difference between the portion of the CU corresponding to theTU and the original block. A TU is not necessarily limited to the sizeof a PU. Thus, TUs may be larger or smaller than a PU. For intra coding,a PU may be collocated with a corresponding leaf-TU for the same CU. Insome examples, the maximum size of a leaf-TU may correspond to the sizeof the corresponding leaf-CU.

Moreover, TUs of leaf-CUs may also be associated with respectivequadtree data structures, referred to as residual quadtrees (RQTs). Thatis, a leaf-CU may include a quadtree indicating how the leaf-CU ispartitioned into TUs. The root node of a TU quadtree generallycorresponds to a leaf-CU, while the root node of a CU quadtree generallycorresponds to a treeblock (or LCU). TUs of the RQT that are not splitare referred to as leaf-TUs. In general, this disclosure uses the termsCU and TU to refer to leaf-CU and leaf-TU, respectively, unless notedotherwise.

A video sequence typically includes a series of video frames orpictures. A group of pictures (GOP) generally comprises a series of oneor more of the video pictures. A GOP may include syntax data in a headerof the GOP, a header of one or more of the pictures, or elsewhere, thatdescribes a number of pictures included in the GOP. Each slice of apicture may include slice syntax data that describes an encoding modefor the respective slice. Video encoder 20 typically operates on videoblocks within individual video slices in order to encode the video data.A video block may correspond to a coding node within a CU. The videoblocks may have fixed or varying sizes, and may differ in size accordingto a specified coding standard.

As an example, the HM supports prediction in various PU sizes. Assumingthat the size of a particular CU is 2N×2N, the HM supportsintra-prediction in PU sizes of 2N×2N or N×N, and inter-prediction insymmetric PU sizes of 2N×2N, 2N×N, N×2N, or N×N. The HM also supportsasymmetric partitioning for inter-prediction in PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In asymmetric partitioning, one direction of aCU is not partitioned, while the other direction is partitioned into 25%and 75%. The portion of the CU corresponding to the 25% partition isindicated by an “n” followed by an indication of “Up”, “Down,” “Left,”or “Right.” Thus, for example, “2N×nU” refers to a 2N×2N CU that ispartitioned horizontally with a 2N×0.5N PU on top and a 2N×1.5N PU onbottom.

In this disclosure, “N×N” and “N by N” may be used interchangeably torefer to the pixel dimensions of a video block in terms of vertical andhorizontal dimensions, e.g., 16×16 pixels or 16 by 16 pixels. Ingeneral, a 16×16 block will have 16 pixels in a vertical direction(y=16) and 16 pixels in a horizontal direction (x=16). Likewise, an N×Nblock generally has N pixels in a vertical direction and N pixels in ahorizontal direction, where N represents a nonnegative integer value.The pixels in a block may be arranged in rows and columns. Moreover,blocks need not necessarily have the same number of pixels in thehorizontal direction as in the vertical direction. For example, blocksmay comprise N×M pixels, where M is not necessarily equal to N.

Following intra-predictive or inter-predictive coding using the PUs of aCU, video encoder 20 may calculate residual data for the TUs of the CU.The PUs may comprise syntax data describing a method or mode ofgenerating predictive pixel data in the spatial domain (also referred toas the pixel domain) and the TUs may comprise coefficients in thetransform domain following application of a transform, e.g., a discretesine transform (DST), a discrete cosine transform (DCT), an integertransform, a wavelet transform, or a conceptually similar transform toresidual video data. The residual data may correspond to pixeldifferences between pixels of the unencoded picture and predictionvalues corresponding to the PUs. Video encoder 20 may form the TUsincluding the residual data for the CU, and then transform the TUs toproduce transform coefficients for the CU.

Following any transforms to produce transform coefficients, videoencoder 20 may perform quantization of the transform coefficients.Quantization is a broad term intended to have its broadest ordinarymeaning. In one embodiment, quantization refers to a process in whichtransform coefficients are quantized to possibly reduce the amount ofdata used to represent the coefficients, providing further compression.The quantization process may reduce the bit depth associated with someor all of the coefficients. For example, an n-bit value may be roundeddown to an m-bit value during quantization, where n is greater than m.

Following quantization, the video encoder may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the array and to place lowerenergy (and therefore higher frequency) coefficients at the back of thearray. In some examples, video encoder 20 may utilize a predefined scanorder to scan the quantized transform coefficients to produce aserialized vector that can be entropy encoded. In other examples, videoencoder 20 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form a one-dimensional vector, video encoder20 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive variable length coding (CAVLC), context-adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), Probability Interval Partitioning Entropy(PIPE) coding or another entropy encoding methodology. Video encoder 20may also entropy encode syntax elements associated with the encodedvideo data for use by video decoder 30 in decoding the video data.

To perform CABAC, video encoder 20 may assign a context within a contextmodel to a symbol to be transmitted. The context may relate to, forexample, whether neighboring values of the symbol are non-zero or not.To perform CAVLC, video encoder 20 may select a variable length code fora symbol to be transmitted. Codewords in VLC may be constructed suchthat relatively shorter codes correspond to more probable symbols, whilelonger codes correspond to less probable symbols. In this way, the useof VLC may achieve a bit savings over, for example, using equal-lengthcodewords for each symbol to be transmitted. The probabilitydetermination may be based on a context assigned to the symbol.

Video encoder 20 may further send syntax data, such as block-basedsyntax data, frame-based syntax data, and GOP-based syntax data, tovideo decoder 30, e.g., in a frame header, a block header, a sliceheader, or a GOP header. The GOP syntax data may describe a number offrames in the respective GOP, and the frame syntax data may indicate anencoding/prediction mode used to encode the corresponding frame.

Video Encoder

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure. Video encoder 20 may be configured to process a singlelayer of a video bitstream, such as for HEVC. Further, video encoder 20may be configured to perform any or all of the techniques of thisdisclosure, including but not limited to the methods of determiningrounding offsets used in resampling process and related processesdescribed in greater detail above and below with respect to FIGS. 4-6.As one example, inter-layer prediction unit 66 (when provided) may beconfigured to perform any or all of the techniques described in thisdisclosure. However, aspects of this disclosure are not so limited. Insome examples, the techniques described in this disclosure may be sharedamong the various components of video encoder 20. In some examples,additionally or alternatively, a processor (not shown) may be configuredto perform any or all of the techniques described in this disclosure.

For purposes of explanation, this disclosure describes video encoder 20in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theencoder 20 of FIG. 2A illustrates a single layer of a codec. However, aswill be described further with respect to FIG. 2B, some or all of thevideo encoder 20 may be duplicated for processing according to amulti-layer codec.

Video encoder 20 may perform intra-, inter-, and inter-layer prediction(sometime referred to as intra-, inter- or inter-layer coding) of videoblocks within video slices. Intra coding relies on spatial prediction toreduce or remove spatial redundancy in video within a given video frameor picture. Inter-coding relies on temporal prediction to reduce orremove temporal redundancy in video within adjacent frames or picturesof a video sequence. Inter-layer coding relies on prediction based uponvideo within a different layer(s) within the same video coding sequence.Intra-mode (I mode) may refer to any of several spatial based codingmodes. Inter-modes, such as uni-directional prediction (P mode) orbi-prediction (B mode), may refer to any of several temporal-basedcoding modes.

As shown in FIG. 2A, video encoder 20 receives a current video blockwithin a video frame to be encoded. In the example of FIG. 2A, videoencoder 20 includes mode select unit 40, reference frame memory 64,summer 50, transform processing unit 52, quantization unit 54, andentropy encoding unit 56. Mode select unit 40, in turn, includes motioncompensation unit 44, motion estimation unit 42, intra-prediction unit46, inter-layer prediction unit 66, and partition unit 48. Referenceframe memory 64 may include a decoded picture buffer. The decodedpicture buffer is a broad term having its ordinary meaning, and in someembodiments refers to a video codec-managed data structure of referenceframes.

For video block reconstruction, video encoder 20 also includes inversequantization unit 58, inverse transform unit 60, and summer 62. Adeblocking filter (not shown in FIG. 2A) may also be included to filterblock boundaries to remove blockiness artifacts from reconstructedvideo. If desired, the deblocking filter would typically filter theoutput of summer 62. Additional filters (in loop or post loop) may alsobe used in addition to the deblocking filter. Such filters are not shownfor brevity, but if desired, may filter the output of summer 50 (as anin-loop filter).

During the encoding process, video encoder 20 receives a video frame orslice to be coded. The frame or slice may be divided into multiple videoblocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive coding of the received video block relative toone or more blocks in one or more reference frames to provide temporalprediction. Intra-prediction unit 46 may alternatively performintra-predictive coding of the received video block relative to one ormore neighboring blocks in the same frame or slice as the block to becoded to provide spatial prediction. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a frame or slice into LCUs, and partition each of the LCUsinto sub-CUs based on rate-distortion analysis (e.g., rate-distortionoptimization, etc.). Mode select unit 40 may further produce a quadtreedata structure indicative of partitioning of an LCU into sub-CUs.Leaf-node CUs of the quadtree may include one or more PUs and one ormore TUs.

Mode select unit 40 may select one of the coding modes, intra, inter, orinter-layer prediction mode, e.g., based on error results, and providethe resulting intra-, inter-, or inter-layer coded block to summer 50 togenerate residual block data and to summer 62 to reconstruct the encodedblock for use as a reference frame. Mode select unit 40 also providessyntax elements, such as motion vectors, intra-mode indicators,partition information, and other such syntax information, to entropyencoding unit 56.

Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference frame (or other coded unit)relative to the current block being coded within the current frame (orother coded unit). A predictive block is a block that is found toclosely match the block to be coded, in terms of pixel difference, whichmay be determined by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics. In some examples, videoencoder 20 may calculate values for sub-integer pixel positions ofreference pictures stored in reference frame memory 64. For example,video encoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in reference frame memory 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Motion estimation unit42 and motion compensation unit 44 may be functionally integrated, insome examples. Upon receiving the motion vector for the PU of thecurrent video block, motion compensation unit 44 may locate thepredictive block to which the motion vector points in one of thereference picture lists. Summer 50 forms a residual video block bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values,as discussed below. In some embodiments, motion estimation unit 42 canperform motion estimation relative to luma components, and motioncompensation unit 44 can use motion vectors calculated based on the lumacomponents for both chroma components and luma components. Mode selectunit 40 may generate syntax elements associated with the video blocksand the video slice for use by video decoder 30 in decoding the videoblocks of the video slice.

Intra-prediction unit 46 may intra-predict or calculate a current block,as an alternative to the inter-prediction performed by motion estimationunit 42 and motion compensation unit 44, as described above. Inparticular, intra-prediction unit 46 may determine an intra-predictionmode to use to encode a current block. In some examples,intra-prediction unit 46 may encode a current block using variousintra-prediction modes, e.g., during separate encoding passes, andintra-prediction unit 46 (or mode select unit 40, in some examples) mayselect an appropriate intra-prediction mode to use from the testedmodes.

For example, intra-prediction unit 46 may calculate rate-distortionvalues using a rate-distortion analysis for the various testedintra-prediction modes, and select the intra-prediction mode having thebest rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bitrate(that is, a number of bits) used to produce the encoded block.Intra-prediction unit 46 may calculate ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block.

After selecting an intra-prediction mode for a block, intra-predictionunit 46 may provide information indicative of the selectedintra-prediction mode for the block to entropy encoding unit 56. Entropyencoding unit 56 may encode the information indicating the selectedintra-prediction mode. Video encoder 20 may include in the transmittedbitstream configuration data, which may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks, andindications of a most probable intra-prediction mode, anintra-prediction mode index table, and a modified intra-prediction modeindex table to use for each of the contexts.

The video encoder 20 may include an inter-layer prediction unit 66.Inter-layer prediction unit 66 is configured to predict a current block(e.g., a current block in the EL) using one or more different layersthat are available in SVC (e.g., a base or reference layer). Suchprediction may be referred to as inter-layer prediction. Inter-layerprediction unit 66 utilizes prediction methods to reduce inter-layerredundancy, thereby improving coding efficiency and reducingcomputational resource requirements. Some examples of inter-layerprediction include inter-layer intra prediction, inter-layer motionprediction, and inter-layer residual prediction. Inter-layer intraprediction uses the reconstruction of co-located blocks in the baselayer to predict the current block in the enhancement layer. Inter-layermotion prediction uses motion information of the base layer to predictmotion in the enhancement layer. Inter-layer residual prediction usesthe residue of the base layer to predict the residue of the enhancementlayer. When the base and enhancement layers have different spatialresolutions, spatial motion vector scaling and/or inter-layer positionmapping using a temporal scaling function may be performed by theinter-layer prediction unit 66, as described in greater detail below.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation. Transform processing unit 52 appliesa transform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform, to the residual block, producing a video blockcomprising residual transform coefficient values. Transform processingunit 52 may perform other transforms which are conceptually similar toDCT. For example, discrete sine transforms (DST), wavelet transforms,integer transforms, sub-band transforms or other types of transforms canalso be used.

Transform processing unit 52 can apply the transform to the residualblock, producing a block of residual transform coefficients. Thetransform may convert the residual information from a pixel value domainto a transform domain, such as a frequency domain. Transform processingunit 52 may send the resulting transform coefficients to quantizationunit 54. Quantization unit 54 quantizes the transform coefficients tofurther reduce bit rate. The quantization process may reduce the bitdepth associated with some or all of the coefficients. The degree ofquantization may be modified by adjusting a quantization parameter. Insome examples, quantization unit 54 may then perform a scan of thematrix including the quantized transform coefficients. Alternatively,entropy encoding unit 56 may perform the scan.

Following quantization, entropy encoding unit 56 entropy encodes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy coding technique. In the caseof context-based entropy coding, context may be based on neighboringblocks. Following the entropy coding by entropy encoding unit 56, theencoded bitstream may be transmitted to another device (e.g., videodecoder 30) or archived for later transmission or retrieval.

Inverse quantization unit 58 and inverse transform unit 60 apply inversequantization and inverse transformation, respectively, to reconstructthe residual block in the pixel domain (e.g., for later use as areference block). Motion compensation unit 44 may calculate a referenceblock by adding the residual block to a predictive block of one of theframes of reference frame memory 64. Motion compensation unit 44 mayalso apply one or more interpolation filters to the reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Summer 62 adds the reconstructed residual block to themotion compensated prediction block produced by motion compensation unit44 to produce a reconstructed video block for storage in reference framememory 64. The reconstructed video block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-code a block in a subsequent video frame.

Multi-Layer Video Encoder

FIG. 2B is a block diagram illustrating an example of a multi-layervideo encoder 21 that may implement techniques in accordance withaspects described in this disclosure. The video encoder 21 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video encoder 21 may be configured toperform any or all of the techniques of this disclosure.

The video encoder 21 includes a video encoder 20A and video encoder 20B,each of which may be configured as the video encoder 20 of FIG. 2A andmay perform the functions described above with respect to the videoencoder 20. Further, as indicated by the reuse of reference numbers, thevideo encoders 20A and 20B may include at least some of the systems andsubsystems as the video encoder 20. Although the video encoder 21 isillustrated as including two video encoders 20A and 20B, the videoencoder 21 is not limited as such and may include any number of videoencoder 20 layers. In some embodiments, the video encoder 21 may includea video encoder 20 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed orencoded by a video encoder that includes five encoder layers. In someembodiments, the video encoder 21 may include more encoder layers thanframes in an access unit. In some such cases, some of the video encoderlayers may be inactive when processing some access units.

In addition to the video encoders 20A and 20B, the video encoder 21 mayinclude a resampling unit 90. The resampling unit 90 may, in some cases,upsample a base layer of a received video frame to, for example, createan enhancement layer. The resampling unit 90 may upsample particularinformation associated with the received base layer of a frame, but notother information. For example, the resampling unit 90 may upsample thespatial size or number of pixels of the base layer, but the number ofslices or the picture order count may remain constant. In some cases,the resampling unit 90 may not process the received video and/or may beoptional. For example, in some cases, the mode select unit 40 mayperform upsampling. In some embodiments, the resampling unit 90 isconfigured to upsample a layer and reorganize, redefine, modify, oradjust one or more slices to comply with a set of slice boundary rulesand/or raster scan rules. Although primarily described as upsampling abase layer, or a lower layer in an access unit, in some cases, theresampling unit 90 may downsample a layer. For example, if duringstreaming of a video bandwidth is reduced, a frame may be downsampledinstead of upsampled. Resampling unit 90 may be further configured toperform cropping and/or padding operations, as well.

The resampling unit 90 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 114 of the lower layer encoder (e.g., the video encoder20A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the mode select unit 40of a higher layer encoder (e.g., the video encoder 20B) configured toencode a picture in the same access unit as the lower layer encoder. Insome cases, the higher layer encoder is one layer removed from the lowerlayer encoder. In other cases, there may be one or more higher layerencoders between the layer 0 video encoder and the layer 1 encoder ofFIG. 2B.

In some cases, the resampling unit 90 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 64 of the videoencoder 20A may be provided directly, or at least without being providedto the resampling unit 90, to the mode select unit 40 of the videoencoder 20B. For example, if video data provided to the video encoder20B and the reference picture from the decoded picture buffer 64 of thevideo encoder 20A are of the same size or resolution, the referencepicture may be provided to the video encoder 20B without any resampling.

In some embodiments, the video encoder 21 downsamples video data to beprovided to the lower layer encoder using the downsampling unit 94before provided the video data to the video encoder 20A. Alternatively,the downsampling unit 94 may be a resampling unit 90 capable ofupsampling or downsampling the video data. In yet other embodiments, thedownsampling unit 94 may be omitted.

As illustrated in FIG. 2B, the video encoder 21 may further include amultiplexor 98, or mux. The mux 98 can output a combined bitstream fromthe video encoder 21. The combined bitstream may be created by taking abitstream from each of the video encoders 20A and 20B and alternatingwhich bitstream is output at a given time. While in some cases the bitsfrom the two (or more in the case of more than two video encoder layers)bitstreams may be alternated one bit at a time, in many cases thebitstreams are combined differently. For example, the output bitstreammay be created by alternating the selected bitstream one block at atime. In another example, the output bitstream may be created byoutputting a non-1:1 ratio of blocks from each of the video encoders 20Aand 20B. For instance, two blocks may be output from the video encoder20B for each block output from the video encoder 20A. In someembodiments, the output stream from the mux 98 may be preprogrammed. Inother embodiments, the mux 98 may combine the bitstreams from the videoencoders 20A, 20B based on a control signal received from a systemexternal to the video encoder 21, such as from a processor on the sourcedevice 12. The control signal may be generated based on the resolutionor bitrate of a video from the video source 18, based on a bandwidth ofthe channel 16, based on a subscription associated with a user (e.g., apaid subscription versus a free subscription), or based on any otherfactor for determining a resolution output desired from the videoencoder 21.

Video Decoder

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure. The video decoder 30 may be configured to process asingle layer of a video bitstream, such as for HEVC. Further, videodecoder 30 may be configured to perform any or all of the techniques ofthis disclosure, including but not limited to the methods of determiningrounding offsets used in resampling process and related processesdescribed in greater detail above and below with respect to FIGS. 4-6.As one example, inter-layer prediction unit 75 may be configured toperform any or all of the techniques described in this disclosure.However, aspects of this disclosure are not so limited. In someexamples, the techniques described in this disclosure may be sharedamong the various components of video decoder 30. In some examples,additionally or alternatively, a processor (not shown) may be configuredto perform any or all of the techniques described in this disclosure.

For purposes of explanation, this disclosure describes video decoder 30in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Thedecoder 30 of FIG. 3A illustrates a single layer of a codec. However, aswill be described further with respect to FIG. 3B, some or all of thevideo decoder 30 may be duplicated for processing according to amulti-layer codec.

In the example of FIG. 3A, video decoder 30 includes an entropy decodingunit 70, motion compensation unit 72, intra prediction unit 74,inter-layer prediction unit 75, inverse quantization unit 76, inversetransformation unit 78, reference frame memory 82 and summer 80. In someembodiments, motion compensation unit 72 and/or intra prediction unit 74may be configured to perform inter-layer prediction, in which case theinter-layer prediction unit 75 may be omitted. Video decoder 30 may, insome examples, perform a decoding pass generally reciprocal to theencoding pass described with respect to video encoder 20 (FIG. 2A).Motion compensation unit 72 may generate prediction data based on motionvectors received from entropy decoding unit 70, while intra-predictionunit 74 may generate prediction data based on intra-prediction modeindicators received from entropy decoding unit 70. Reference framememory 82 may include a decoded picture buffer. The decoded picturebuffer is a broad term having its ordinary meaning, and in someembodiments refers to a video codec-managed data structure of referenceframes.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit70 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 70 forwardsthe motion vectors to and other syntax elements to motion compensationunit 72. Video decoder 30 may receive the syntax elements at the videoslice level and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intraprediction unit 74 may generate prediction data for a video block of thecurrent video slice based on a signaled intra prediction mode and datafrom previously decoded blocks of the current frame or picture. When thevideo frame is coded as an inter-coded (e.g., B, P or GPB) slice, motioncompensation unit 72 produces predictive blocks for a video block of thecurrent video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 70. The predictive blocksmay be produced from one of the reference pictures within one of thereference picture lists. Video decoder 30 may construct the referenceframe lists, List 0 and List 1, using default construction techniquesbased on reference pictures stored in reference frame memory 82.

Motion compensation unit 72 determines prediction information for avideo block of the current video slice by parsing the motion vectors andother syntax elements, and uses the prediction information to producethe predictive blocks for the current video block being decoded. Forexample, motion compensation unit 72 uses some of the received syntaxelements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter-encoded video block of theslice, inter-prediction status for each inter-coded video block of theslice, and other information to decode the video blocks in the currentvideo slice.

Motion compensation unit 72 may also perform interpolation based oninterpolation filters. Motion compensation unit 72 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. In this case, motion compensation unit 72 may determine theinterpolation filters used by video encoder 20 from the received syntaxelements and use the interpolation filters to produce predictive blocks.

Video decoder 30 may also include an inter-layer prediction unit 75. Theinter-layer prediction unit 75 is configured to predict a current block(e.g., a current block in the EL) using one or more different layersthat are available in SVC (e.g., a base or reference layer). Suchprediction may be referred to as inter-layer prediction. Inter-layerprediction unit 75 utilizes prediction methods to reduce inter-layerredundancy, thereby improving coding efficiency and reducingcomputational resource requirements. Some examples of inter-layerprediction include inter-layer intra prediction, inter-layer motionprediction, and inter-layer residual prediction. Inter-layer intraprediction uses the reconstruction of co-located blocks in the baselayer to predict the current block in the enhancement layer. Inter-layermotion prediction uses motion information of the base layer to predictmotion in the enhancement layer. Inter-layer residual prediction usesthe residue of the base layer to predict the residue of the enhancementlayer. When the base and enhancement layers have different spatialresolutions, spatial motion vector scaling and/or inter-layer positionmapping may be performed by the inter-layer prediction unit 75 using atemporal scaling function, as described in greater detail below.

Inverse quantization unit 76 inverse quantizes, e.g., de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 70. The inverse quantization process mayinclude use of a quantization parameter QPY calculated by video decoder30 for each video block in the video slice to determine a degree ofquantization and, likewise, a degree of inverse quantization that shouldbe applied.

Inverse transform unit 78 applies an inverse transform, e.g., an inverseDCT, an inverse DST, an inverse integer transform, or a conceptuallysimilar inverse transform process, to the transform coefficients inorder to produce residual blocks in the pixel domain.

After motion compensation unit 72 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform unit 78 with the correspondingpredictive blocks generated by motion compensation unit 72. Summer 90represents the component or components that perform this summationoperation. If desired, a deblocking filter may also be applied to filterthe decoded blocks in order to remove blockiness artifacts. Other loopfilters (either in the coding loop or after the coding loop) may also beused to smooth pixel transitions, or otherwise improve the videoquality. The decoded video blocks in a given frame or picture are thenstored in reference frame memory 82, which stores reference picturesused for subsequent motion compensation. Reference frame memory 82 alsostores decoded video for later presentation on a display device, such asdisplay device 32 of FIG. 1.

Multi-Layer Decoder

FIG. 3B is a block diagram illustrating an example of a multi-layervideo decoder 31 that may implement techniques in accordance withaspects described in this disclosure. The video decoder 31 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video decoder 31 may be configured toperform any or all of the techniques of this disclosure.

The video decoder 31 includes a video decoder 30A and video decoder 30B,each of which may be configured as the video decoder 30 of FIG. 3A andmay perform the functions described above with respect to the videodecoder 30. Further, as indicated by the reuse of reference numbers, thevideo decoders 30A and 30B may include at least some of the systems andsubsystems as the video decoder 30. Although the video decoder 31 isillustrated as including two video decoders 30A and 30B, the videodecoder 31 is not limited as such and may include any number of videodecoder 30 layers. In some embodiments, the video decoder 31 may includea video decoder 30 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed ordecoded by a video decoder that includes five decoder layers. In someembodiments, the video decoder 31 may include more decoder layers thanframes in an access unit. In some such cases, some of the video decoderlayers may be inactive when processing some access units.

In addition to the video decoders 30A and 30B, the video decoder 31 mayinclude an upsampling unit 92. In some embodiments, the upsampling unit92 may upsample a base layer of a received video frame to create anenhanced layer to be added to the reference picture list for the frameor access unit. This enhanced layer can be stored in the reference framememory 82 (e.g., in its decoded picture buffer, etc.). In someembodiments, the upsampling unit 92 can include some or all of theembodiments described with respect to the resampling unit 90 of FIG. 2B.In some embodiments, the upsampling unit 92 is configured to upsample alayer and reorganize, redefine, modify, or adjust one or more slices tocomply with a set of slice boundary rules and/or raster scan rules. Insome cases, the upsampling unit 92 may be a resampling unit configuredto upsample and/or downsample a layer of a received video frame.

The upsampling unit 92 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 82 of the lower layer decoder (e.g., the video decoder30A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the mode select unit 71of a higher layer decoder (e.g., the video decoder 30B) configured todecode a picture in the same access unit as the lower layer decoder. Insome cases, the higher layer decoder is one layer removed from the lowerlayer decoder. In other cases, there may be one or more higher layerdecoders between the layer 0 decoder and the layer 1 decoder of FIG. 3B.

In some cases, the upsampling unit 92 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 82 of the videodecoder 30A may be provided directly, or at least without being providedto the upsampling unit 92, to the mode select unit 71 of the videodecoder 30B. For example, if video data provided to the video decoder30B and the reference picture from the decoded picture buffer 82 of thevideo decoder 30A are of the same size or resolution, the referencepicture may be provided to the video decoder 30B without upsampling.Further, in some embodiments, the upsampling unit 92 may be a resamplingunit 90 configured to upsample or downsample a reference picturereceived from the decoded picture buffer 82 of the video decoder 30A.

As illustrated in FIG. 3B, the video decoder 31 may further include ademultiplexor 99, or demux. The demux 99 can split an encoded videobitstream into multiple bitstreams with each bitstream output by thedemux 99 being provided to a different video decoder 30A and 30B. Themultiple bitstreams may be created by receiving a bitstream and each ofthe video decoders 30A and 30B receives a portion of the bitstream at agiven time. While in some cases the bits from the bitstream received atthe demux 99 may be alternated one bit at a time between each of thevideo decoders (e.g., video decoders 30A and 30B in the example of FIG.3B), in many cases the bitstream is divided differently. For example,the bitstream may be divided by alternating which video decoder receivesthe bitstream one block at a time. In another example, the bitstream maybe divided by a non-1:1 ratio of blocks to each of the video decoders30A and 30B. For instance, two blocks may be provided to the videodecoder 30B for each block provided to the video decoder 30A. In someembodiments, the division of the bitstream by the demux 99 may bepreprogrammed. In other embodiments, the demux 99 may divide thebitstream based on a control signal received from a system external tothe video decoder 31, such as from a processor on the destination device14. The control signal may be generated based on the resolution orbitrate of a video from the input interface 28, based on a bandwidth ofthe channel 16, based on a subscription associated with a user (e.g., apaid subscription versus a free subscription), or based on any otherfactor for determining a resolution obtainable by the video decoder 31.

Resampling Process in SHVC

In SHVC, if a reference layer picture size is different from theenhancement layer picture size, a resampling (or upsampling) process canbe applied to the reference layer picture to match the size of theenhancement layer picture for inter-layer prediction. To resample thereference layer picture, an N tap resampling filter can be applied foreach color component.

In the filtering process, the samples (or pixels) magnitudes of thereference layer picture can be multiplied by filter coefficients andsummed up to derive a filtered sample (or pixel). Since the size of thereference layer picture and the size of the enhancement layer pictureare different, the coordinates of the reference layer samples involvedin the filtering process may be defined. For example, the samplelocation of the reference layer picture that corresponds to the samplelocation of the current enhancement layer picture can be determined sothat sample(s) indicated by the sample location of the reference layerpicture can be used in the resampling process. In one embodiment, thisprocess can be referred to as sample position mapping or sample locationdetermination, which is further described below.

SHVC includes a section relating to derivation process for referencelayer sample location used in resampling (e.g., Section G6.1). Theprocess can take as an input a sample location relative to the top-leftsample of the color component of the current picture and output a samplelocation specifying the reference layer sample location in units offractional sample (e.g., 1/12th, 1/16th sample) relative to the top-leftsample of the reference layer picture.

During the process of reference layer sample location, an additionalrounding offset can be applied. Rounding offsets can be added indetermining the sample location of the reference layer picture to beresampled. For example, an additional rounding offset addY can beapplied in the vertical direction. Similarly, an additional roundingoffset addX can be applied in the horizontal direction. The roundingoffset addY and the rounding offset addX may also be referred to as thevertical rounding offset and the horizontal rounding offset,respectively. The sample location of the reference layer picture can bedefined by a horizontal sample location and a vertical sample location.The horizontal rounding offset can be added in determining thehorizontal sample location of the reference layer picture forresampling, and the vertical rounding offset can be added in determiningthe vertical sample location of the reference layer picture forresampling.

In SHVC, scaling factors are calculated in the coding process and aregenerally available at the time of calculating the rounding offsetsbefore invoking reference layer sample location derivation process. Forexample, they can be generated in Section G8.1.4, the resampling processfor inter layer reference pictures. The scaling factors can include ahorizontal scaling factor ScaleFactorX and a vertical scaling factorScaleFactorY. The scaling factors may be calculated for the currentenhancement layer picture. The horizontal scaling factor and thevertical scaling factor may indicate the proportion of scaling betweenthe reference layer picture and the enhancement layer picture in thehorizontal direction and the proportion of scaling between the referencelayer picture and the enhancement layer picture in the verticaldirection, respectively.

In the Working Draft 2 of SHVC, calculating the rounding offsets involvea division operation. However, a division operation can be expensive.Since the calculation for the scaling factors is similar to calculationfor the rounding offsets, the techniques can utilize the scaling factorsin calculating the rounding offsets. Accordingly, the techniquesdescribed in this disclosure can calculate the rounding offsets used inresampling of the reference layer picture without performing a divisionoperation by using the previously calculated scaling factors. Since adivision operation is expensive, the rounding offsets can be calculatedmore efficiently by eliminating a division operation. As a result, thecoding process can be performed more efficiently as well. Certaindetails relating to the techniques are described below with reference toFIG. 4.

FIG. 4 is a block diagram illustrating an example of determiningrounding offsets used in resampling process, according to aspects of thedisclosure. Various term used throughout this disclosure are broad termshaving their ordinary meaning. In addition, in some embodiments, certainterms relate to the following video concepts. In certain embodiments, arounding offset can refer to a value that is added in a calculationprocess to round a predetermined value. In certain embodiments, thesymbol “*” indicates multiplication, and the symbol “>>” refers toright-shifting of bits. In some embodiments, right shifting and leftshifting of n bits can be implemented as dividing and multiplying by2^n, respectively.

In the Working Draft 2 of SHVC (section G6.1), addY is calculated asfollows:addY=(((RefLayerPicHeightInSamplesL*phaseY)<<14)+(ScaledRefLayerPicHeightInSamplesL>>1))/ScaledRefLayerPicHeightInSamplesL,where RefLayerPicHeightInSamplesL 418 indicates the height of thereference layer picture 410 and ScaledRefLayerPicHeightInSamplesL 432indicates the height of the scaled or resampled version of the referencelayer picture 422. However, using a division operation to calculate addYcan be expensive.

Similarly, although addX is not included in the Working Draft 2 of SHVC,addX can be calculated as follows:addX=(((RefLayerPicWidthInSamplesL*phaseX)<<14)+(ScaledRefLayerPicWidthInSamplesL>>1))/ScaledRefLayerPicWidthInSamplesL,where RefLayerPicWidthInSamplesL 416 indicates the width of thereference layer picture 410 and ScaledRefLayerPicWidthInSamplesL 430indicates the width of the scaled or resampled version of the referencelayer picture 422. Similarly, using a division operation to calculateaddX can be expensive.

In SHVC, ScaleFactorX and ScaleFactorY may be calculated as follows:ScaleFactorX=((RefLayerPicWidthInSamplesL<<16)+(ScaledRefLayerPicWidthInSamplesL>>1))/ScaledRefLayerPicWidthInSamplesLScaleFactorY=((RefLayerPicHeightInSamplesL<<16)+(ScaledRefLayerPicHeightInSamplesL>>1))/ScaledRefLayerPicHeightInSamplesL,where RefLayerPicWidthInSamplesL 416 and RefLayerPicHeightInSamplesL 418indicate the width and the height of the reference layer picture 410,respectively, and ScaledRefLayerPicWidthInSamplesL 430 andScaledRefLayerPicHeightInSamplesL 432 indicate the width and the heightof the scaled or resampled version of the reference layer picture 422,respectively. The ScaledRefLayerPicWidthInSamplesL 430 andScaledRefLayerPicHeightInSamplesL 432 can be explained to indicate thewidth and the height of the scaled or resampled version of the referencelayer picture 422. If the scaled reference layer offsets 424 are zero,ScaledRefLayerPicWidthInSamplesL 430 andScaledRefLayerPicHeightInSamplesL 432 are the same as the width and theheight of the enhancement layer picture 420. Scaled reference layeroffsets 424 may be offsets that indicate, relative to the currentpicture, the region of the upsampled or resampled interlayer referencepicture used in prediction (e.g., when only a portion or region of theupsampled or resampled reference layer picture is used).

The rounding offsets can be used in the derivation process for referencelayer sample location used in resampling. For example, the roundingoffset addY can be used in the derivation process for reference layersample location used in resampling as explained in Section G6.1 of theWorking Draft 2 of SHVC. Details relating to Section G6.1 are explainedbelow:

-   -   Inputs to this process are:        -   a variable cIdx specifying the color component index, and        -   a sample location (xP, yP) 434 relative to the top-left            sample of the color component of the current picture            specified by cIdx.    -   Output of this process is:        -   a sample location (xRef16, yRef16) specifying the reference            layer sample location in units of 1/16-th sample relative to            the top-left sample of the reference layer picture.

The variables used in the derivation process of G.6.1 are explainedbelow:

-   -   Variables offsetX and offsetY can refer to the horizontal and        vertical offsets, respectively, for a color component between        the top-left sample of the associated resampled reference layer        picture and the top-left luma sample of the current enhancement        layer picture. Variables offsetX and offsetY are derived as        follows:        offsetX=ScaledRefLayerLeftOffset/((cIdx==0)?1:SubWidthC)   (G-3)        offsetY=ScaledRefLayerTopOffset/((cIdx==0)?1:SubHeightC)          (G-4),        where ScaledRefLayerLeftOffset 424 a indicates the left offset        of a luma color component, Scaled ScaledRefLayerTopOffset 424 b        indicates the top offset of the luma color component, SubWidthC        indicates the chroma color component sub-sampling relative to        the luma color component in the horizontal direction, and        SubHeightC indicates the chroma color component sub-sampling        relative to the luma color component in the vertical direction,        and cIdx represents the color component index and can be equal        to 0. For example, cIdx is equal to 0 for the luma color        component and is greater than 0 for chroma color components.    -   Variable phaseY can refer to a resampling filter phase of the        luma color component. Variables phaseY can be derived as        follows:        phaseY=(cIdx==0)?0:1   (G-5).    -   Variable addY is explained above and can be derived as follows:        addY=(((RefLayerPicHeightInSamplesL*phaseY)<<14)+(ScaledRefLayerPicHeightInSamplesL>>1))/ScaledRefLayerPicHeightInSamplesL  (G-6)    -   Variables xRef16 and yRef16 can refer to a sample location        specifying the reference layer sample location in units of        1/16-th sample relative to the top-left sample of the reference        layer picture. Variable xRef16 can refer to the horizontal        sample location, and variable yRef16 can refer to the vertical        sample location. Variables xRef16 and yRef16 are derived as        follows:        xRef16=(((xP−offsetX)*ScaleFactorX+(1<<11))>>12)  (G-7)        yRef16=(((yP−offsetY)*ScaleFactorY+addY+(1<<11))>>12)−(phaseY−2)  (G-8)

As shown above, the calculation for the scaling factors is similar tocalculation for the rounding offsets. Accordingly, the techniques canutilize the scaling factors in calculating the rounding offsets to avoidperforming another division operation. For example, ScaleFactorX andScaleFactorY calculated for the sample location derivation in theresampling process can be used for the additional rounding offsetcalculation. In one embodiment, addY and addX can be calculated asfollows:addY=(ScaleFactorY*phaseY+offset)>>2addX=(ScaleFactorX*phaseX+offset)>>2,wherein the variable “offset” refers to a rounding offset, which can besome number (e.g., 0, 1, 2, etc.).

Although addX is not used in the Working Draft 2, addX can be calculatedin a similar manner as addY as specified above, and xRef16 can bederived in a similar manner as yRef16 as follows:xRef16=(((xP−offsetX)*ScaleFactorX+addX+(1<<11))>>12)−(phaseX<<2),where phaseX can be determined in a similar manner as phaseY.

In some embodiments, modified addX and addY can be included directly inthe xRef16 and yRef16 calculation. For example, yRef16 can be calculatedas follows:yRef16=((((yP−offsetY)*4+phaseY)*ScaleFactorY+(1<<13))>>14)−(phaseY<<2)In some cases, incorporating addY directly into the calculation ofyRef16 can lead to increased accuracy.

The above examples have been described in terms of 1/16th sampleaccuracy. However, different units of fractional accuracy can be used,for example 1/12th or similar.

Generally, the scaling factors are available when the rounding offsetsare calculated, and therefore, the rounding offsets can be calculatedbased on the scaling factors without performing a division operation.Since a division operation is expensive, the rounding offsets can becalculated more efficiently by eliminating a division operation. As aresult, the coding process can be performed more efficiently as well.

All features and/or embodiments described with respect to FIG. 4 may beimplemented alone or in any combination with other features and/orembodiments described in FIGS. 4-6.

Method of Determining Rounding Offset Values Used in Resampling ofReference Layer Picture

FIG. 5 is a flowchart illustrating one embodiment of a method fordetermining rounding offsets used in resampling process, according toaspects of this disclosure. The process 500 may be performed by anencoder (e.g., the encoder as shown in FIG. 2A, 2B, etc.), a decoder(e.g., the decoder as shown in FIG. 3A, 3B, etc.), or any othercomponent, depending on the embodiment. The blocks of the process 500are described with respect to the decoder 31 in FIG. 3B, but the process500 may be performed by other components, such as an encoder, asmentioned above. The layer 1 video decoder 30B of the decoder 31 and/orthe layer 0 decoder 30A of the decoder 31 may perform the process 500,depending on the embodiment. All embodiments described with respect toFIG. 5 may be implemented separately, or in combination with oneanother. Certain details relating to the process 500 are explained aboveand below, e.g., with respect to FIGS. 4 and 6.

The process 500 starts at block 501. The decoder 31 can include a memory(e.g., reference frame memory 82) for storing video informationassociated with a reference layer picture and an enhancement layerpicture.

At block 502, the decoder 31 receives a scale factor that indicates aproportion of scaling between the reference layer picture and theenhancement layer picture in a first direction. The first direction maybe the horizontal direction or the vertical direction. For example, thescale factor can be for the horizontal direction or the verticaldirection. In some embodiments, the first direction is the horizontaldirection and the scale factor is based on a width of the referencelayer picture and a width of the enhancement layer picture. In otherembodiments, the first direction is the horizontal direction and thescale factor is based on a width of the reference layer picture and awidth of a scaled version of the reference layer picture. In certainembodiments, the scale factor in the horizontal direction is determinedas (1) a sum of (a) the width of the reference layer picture shiftedleft by 16 bits and (b) the width of the scaled version of the referencelayer picture shifted right by 1 bit, divided by (2) the width of thescaled version of the reference layer picture.

In some embodiments, the first direction is the vertical direction andthe scale factor is based on a height of the reference layer picture anda height of the enhancement layer picture. In other embodiments, thefirst direction is the vertical direction and the scale factor is basedon a height of the reference layer picture and a height of a scaledversion of the reference layer picture. In certain embodiments, thescale factor in the vertical direction is determined as (3) a sum of (c)the height of the reference layer picture shifted left by 16 bits and(d) the height of the scaled version of the reference layer pictureshifted right by 1 bit, divided by (4) the height of the scaled versionof the reference layer picture.

At block 503, the decoder 31 determines, without performing a divisionoperation, a rounding offset value using the scale factor. The roundingoffset value may be used in position calculation in a resamplingprocess. The rounding offset value can be for the horizontal directionwhen the scale factor is for the horizontal direction. Similarly, therounding offset value can be for the vertical direction when the scalefactor is for the vertical direction. In some embodiments, the decoder31 determines the rounding offset value as:

-   -   (the scale factor*a phase+a first offset value)>>2, wherein the        phase indicates a resampling filter phase in the first direction        and the first offset value indicates a rounding offset.

At block 504, the decoder 31 determines a coordinate in the firstdirection of a first sample located in the reference layer picture thatcorresponds to a second sample located in the enhancement layer pictureusing the scale factor and the rounding offset value. For example, ifthe scale factor and the rounding offset value are for the horizontaldirection, the coordinate of the first sample can be the horizontalcoordinate. Similarly, if the scale factor and the rounding offset valueare for the vertical direction, the coordinate of the first sample canbe the vertical coordinate. In some embodiments, the horizontalcoordinate and the vertical coordinate of the first sample can indicatethe sample(s) in the reference layer picture that should be includedinto the resampling process.

In some embodiments, the coordinate in the horizontal direction of thefirst sample corresponds to a horizontal coordinate of the secondsample, wherein the coordinate in the horizontal direction of the firstsample is relative to the top-left sample of the reference layer pictureand the horizontal coordinate of the second sample is relative to thetop-left sample of the enhancement layer picture. In other embodiments,the coordinate in the vertical direction of the first sample correspondsto a vertical coordinate of the second sample, wherein the coordinate inthe vertical direction of the first sample is relative to the top-leftsample of the reference layer picture and the vertical coordinate of thesecond sample is relative to the top-left sample of the enhancementlayer picture.

In certain embodiments, the coordinate in the horizontal direction ofthe first sample is determined according to the equation:(((the coordinate in the horizontal direction of the second sample−afirst horizontal offset)*the scale factor in the horizontaldirection+the rounding offset value+(1<<11))>>12)−(a horizontalphase<<2),

-   -   wherein the horizontal phase indicates a resampling filter phase        in the horizontal direction and the first horizontal offset        indicates a horizontal offset for a color coordinate between a        top-left sample of a resampled version of the reference layer        picture and the top-left sample of the enhancement layer        picture.

In other embodiments, the coordinate in the vertical direction of thefirst sample is determined according to the equation:(((the coordinate in the vertical direction of the second sample−a firstvertical offset)*the scale factor+the rounding offsetvalue+(1<<11))>>12)−(a vertical phase<<2),

-   -   wherein the vertical phase indicates a resampling filter phase        in the vertical direction and the first vertical offset        indicates a vertical offset for a color coordinate between a        top-left sample of a resampled version of the reference layer        picture and the top-left sample of the enhancement layer        picture.

The decoder 31 can resample the first sample by applying a resamplingfilter to the first sample.

The process 500 ends at block 505. Blocks may be added and/or omitted inthe process 500, depending on the embodiment, and blocks of the process500 may be performed in different orders, depending on the embodiment.

Any features and/or embodiments described with respect to resampling inthis disclosure may be implemented separately or in any combinationthereof. For example, any features and/or embodiments described inconnection with FIGS. 4 and 6 may be implemented in any combination withany features and/or embodiments described in connection with FIG. 5, andvice versa.

FIG. 6 is a flowchart illustrating a method for determining roundingoffsets used in resampling process, according to aspects of thisdisclosure. The process 600 may be performed by an encoder (e.g., theencoder as shown in FIG. 2A, 2B, etc.), a decoder (e.g., the decoder asshown in FIG. 3A, 3B, etc.), or any other component, depending on theembodiment. The blocks of the process 600 are described with respect tothe decoder 31 in FIG. 3B, but the process 600 may be performed by othercomponents, such as an encoder, as mentioned above. The layer 1 videodecoder 30B of the decoder 31 and/or the layer 0 decoder 30A of thedecoder 31 may perform the process 600, depending on the embodiment. Allembodiments described with respect to FIG. 6 may be implementedseparately, or in combination with one another. Certain details relatingto the process 600 are explained above, e.g., with respect to FIGS. 4and 5.

The process 600 starts at block 601. The decoder 31 can include a memory(e.g., reference frame memory 82) for storing video informationassociated with a reference layer picture in a reference layer and anenhancement layer picture to be coded in an enhancement layer.

At block 602, the decoder 31 determines a horizontal rounding offsetvalue using a horizontal scale factor without performing a divisionoperation. The horizontal rounding offset value may be a rounding offsetvalue used in determining a horizontal sample location of the referencelayer picture in the resampling process applied to the reference layerpicture. The horizontal scale factor can indicate a proportion ofhorizontal scaling between the reference layer picture and theenhancement layer picture.

The horizontal scale factor can be based on the width of the referencelayer picture and the width of a scaled version of the reference layerpicture. In one embodiment, the horizontal scale factor can be based onthe width of the reference layer picture and the width of theenhancement layer picture (e.g., when scaled reference layer offsets are0). In certain embodiments, the horizontal scale factor can bedetermined as: a sum of (a) the width of the reference layer pictureshifted left by 16 bits and (b) a width of the scaled version of thereference layer picture shifted right by 1 bit, the sum divided by thewidth of the scaled version of the reference layer picture.

At block 603, the decoder 31 determines a vertical rounding offset valueusing a vertical scale factor without performing a division operation.The vertical rounding offset value may be a rounding offset value usedin determining a vertical sample location of the reference layer picturein the resampling process applied to the reference layer picture. Thevertical scale factor can indicate a proportion of vertical scalingbetween the reference layer picture and the enhancement layer picture.

The vertical scale factor can be based on the height of the referencelayer picture and the height of the scaled version of the referencelayer picture. In one embodiment, the vertical scale factor can be basedon the height of the reference layer picture and the height of theenhancement layer picture (e.g., when scaled reference layer offsets are0). In certain embodiments, the vertical scale factor can be determinedas a sum of (c) the height of the reference layer picture shifted leftby 16 bits and (d) the height of the scaled version of the referencelayer picture shifted right by 1 bit, the sum divided by the height ofthe scaled version of the reference layer picture.

In some embodiments, the decoder 31 determines the horizontal roundingoffset value as:(the horizontal scale factor*a horizontal phase+a first offsetvalue)>>2,

-   -   wherein the horizontal phase indicates the resampling filter        phase in the horizontal direction and the first offset value        indicates a rounding offset.        The decoder 31 determines the vertical rounding offset value is        determined as:        (the vertical scale factor*a vertical phase+a second offset        value)>>2,    -   wherein the vertical phase indicates the resampling filter phase        in the vertical direction and the second offset value indicates        a rounding offset.

At block 604, the decoder 31 determines a first horizontal samplelocation of the reference layer picture based at least in part on thehorizontal scale factor and the horizontal rounding offset value. In oneembodiment, the first horizontal sample location of the reference layerpicture corresponds to a horizontal sample location of the enhancementlayer picture, wherein the first horizontal sample location is relativeto a top-left sample of the reference layer picture, and wherein thehorizontal sample location of the enhancement layer picture is relativeto a top-left sample of the enhancement layer picture.

In some embodiments, the first horizontal sample location is determinedaccording to the equation:(((the horizontal sample location of the enhancement layer picture−afirst horizontal offset)*the horizontal scale factor+the horizontalrounding offset value+(1<<11))>>12)−(the horizontal phase<<2),

wherein the first horizontal offset indicates a horizontal offset for acolor component between the top-left sample of the resampled version ofthe reference layer picture and the top-left sample of the enhancementlayer picture.

At block 605, the decoder 31 determines a first vertical sample locationof the reference layer picture based at least in part on the verticalscale factor and the vertical rounding offset value. The firsthorizontal sample location and the first vertical sample locationtogether can indicate the sample location of the reference layer pictureto resample in the resampling process applied to the reference layerpicture. The decoder 31 can apply a resampling filter to the samplelocation of the reference layer picture.

In one embodiment, the first vertical sample location of the referencelayer picture corresponds to a vertical sample location of theenhancement layer picture, wherein the first vertical sample location isrelative to the top-left sample of the reference layer picture, andwherein the vertical sample location of the enhancement layer picture isrelative to the top-left sample of the enhancement layer picture.

In some embodiments, the first vertical sample location is determinedaccording to the equation:(((the vertical sample location of the enhancement layer picture−a firstvertical offset)*the vertical scale factor+the vertical rounding offsetvalue+(1<<11))>>12)−(the vertical phase<<2),

wherein the first vertical offset indicates a vertical offset for acolor component between the top-left sample of the resampled version ofthe reference layer picture and the top-left sample of the enhancementlayer picture.

The process 600 ends at block 606. Blocks may be added and/or omitted inthe process 600, depending on the embodiment, and blocks of the process500 may be performed in different orders, depending on the embodiment.

Any features and/or embodiments described with respect to resampling inthis disclosure may be implemented separately or in any combinationthereof. For example, any features and/or embodiments described inconnection with FIGS. 4 and 5 may be implemented in any combination withany features and/or embodiments described in connection with FIG. 6, andvice versa.

Terminology

While the above disclosure has described particular embodiments, manyvariations are possible. For example, as mentioned above, the abovetechniques may be applied to 3D video encoding. In some embodiments of3D video, a reference layer (e.g., a base layer) includes videoinformation sufficient to display a first view of a video and theenhancement layer includes additional video information relative to thereference layer such that the reference layer and the enhancement layertogether include video information sufficient to display a second viewof the video. These two views can used to generate a stereoscopic image.As discussed above, motion information from the reference layer can beused to identify additional implicit hypothesis when encoding ordecoding a video unit in the enhancement layer, in accordance withaspects of the disclosure. This can provide greater coding efficiencyfor a 3D video bitstream.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

Information and signals disclosed herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof. Such techniques may beimplemented in any of a variety of devices such as general purposescomputers, wireless communication device handsets, or integrated circuitdevices having multiple uses including application in wirelesscommunication device handsets and other devices. Any features describedas modules or components may be implemented together in an integratedlogic device or separately as discrete but interoperable logic devices.If implemented in software, the techniques may be realized at least inpart by a computer-readable data storage medium comprising program codeincluding instructions that, when executed, performs one or more of themethods described above. The computer-readable data storage medium mayform part of a computer program product, which may include packagingmaterials. The computer-readable medium may comprise memory or datastorage media, such as random access memory (RAM) such as synchronousdynamic random access memory (SDRAM), read-only memory (ROM),non-volatile random access memory (NVRAM), electrically erasableprogrammable read-only memory (EEPROM), FLASH memory, magnetic oroptical data storage media, and the like. The techniques additionally,or alternatively, may be realized at least in part by acomputer-readable communication medium that carries or communicatesprogram code in the form of instructions or data structures and that canbe accessed, read, and/or executed by a computer, such as propagatedsignals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor,” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured for encodingand decoding, or incorporated in a combined video encoder-decoder(CODEC).

The coding techniques discussed herein may be embodiment in an examplevideo encoding and decoding system. A system includes a source devicethat provides encoded video data to be decoded at a later time by adestination device. In particular, the source device provides the videodata to destination device via a computer-readable medium. The sourcedevice and the destination device may comprise any of a wide range ofdevices, including desktop computers, notebook (i.e., laptop) computers,tablet computers, set-top boxes, telephone handsets such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, or the like. In some cases, the source device and thedestination device may be equipped for wireless communication.

The destination device may receive the encoded video data to be decodedvia the computer-readable medium. The computer-readable medium maycomprise any type of medium or device capable of moving the encodedvideo data from source device to destination device. In one example,computer-readable medium may comprise a communication medium to enablesource device 12 to transmit encoded video data directly to destinationdevice in real-time. The encoded video data may be modulated accordingto a communication standard, such as a wireless communication protocol,and transmitted to destination device. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device to destination device.

In some examples, encoded data may be output from output interface to astorage device. Similarly, encoded data may be accessed from the storagedevice by input interface. The storage device may include any of avariety of distributed or locally accessed data storage media such as ahard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device. Destinationdevice may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In one example the source device includes a video source, a videoencoder, and a output interface. The destination device may include aninput interface, a video decoder, and a display device. The videoencoder of source device may be configured to apply the techniquesdisclosed herein. In other examples, a source device and a destinationdevice may include other components or arrangements. For example, thesource device may receive video data from an external video source, suchas an external camera. Likewise, the destination device may interfacewith an external display device, rather than including an integrateddisplay device.

The example system above merely one example. Techniques for processingvideo data in parallel may be performed by any digital video encodingand/or decoding device. Although generally the techniques of thisdisclosure are performed by a video encoding device, the techniques mayalso be performed by a video encoder/decoder, typically referred to as a“CODEC.” Moreover, the techniques of this disclosure may also beperformed by a video preprocessor. Source device and destination deviceare merely examples of such coding devices in which source devicegenerates coded video data for transmission to destination device. Insome examples, the source and destination devices may operate in asubstantially symmetrical manner such that each of the devices includevideo encoding and decoding components. Hence, example systems maysupport one-way or two-way video transmission between video devices,e.g., for video streaming, video playback, video broadcasting, or videotelephony.

The video source may include a video capture device, such as a videocamera, a video archive containing previously captured video, and/or avideo feed interface to receive video from a video content provider. Asa further alternative, the video source may generate computergraphics-based data as the source video, or a combination of live video,archived video, and computer-generated video. In some cases, if videosource is a video camera, source device and destination device may formso-called camera phones or video phones. As mentioned above, however,the techniques described in this disclosure may be applicable to videocoding in general, and may be applied to wireless and/or wiredapplications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by the video encoder. Theencoded video information may then be output by output interface ontothe computer-readable medium.

As noted the computer-readable medium may include transient media, suchas a wireless broadcast or wired network transmission, or storage media(that is, non-transitory storage media), such as a hard disk, flashdrive, compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from the source device and provide theencoded video data to the destination device, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from the source device and produce a disc containing the encodedvideo data. Therefore, the computer-readable medium may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

The input interface of the destination device receives information fromthe computer-readable medium. The information of the computer-readablemedium may include syntax information defined by the video encoder,which is also used by the video decoder, that includes syntax elementsthat describe characteristics and/or processing of blocks and othercoded units, e.g., group of pictures (GOP). A display device displaysthe decoded video data to a user, and may comprise any of a variety ofdisplay devices such as a cathode ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device. Various embodiments of theinvention have been described. These and other embodiments are withinthe scope of the following claims.

Various embodiments of the invention have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. An apparatus for coding video information, theapparatus comprising: a memory configured to store video data associatedwith a reference layer picture and an enhancement layer picture; and aprocessor operationally coupled to the memory and configured to: receivea scale factor that indicates a proportion of scaling between thereference layer picture and the enhancement layer picture in a firstdirection; determine, based at least in part on the scale factor, arounding offset value for determining a coordinate in the firstdirection of a first sample in the reference layer picture based atleast in part on a coordinate in the first direction of a second samplein the enhancement layer picture that corresponds to the first sample,the rounding offset value further determined in an operation without adivision operator, wherein the rounding offset value is furtherdetermined as a sum that is bit-shifted by an integer value, the sumdetermined based on a summation of (i) a product of the scale factor anda phase and (ii) a first offset value; determine the coordinate in thefirst direction of the first sample using the scale factor and therounding offset value; and encode or decode the enhancement layerpicture based on the first sample at the determined coordinate.
 2. Theapparatus of claim 1, wherein the first direction is a horizontaldirection or a vertical direction.
 3. The apparatus of claim 1, whereinthe processor is further configured to determine the rounding offsetvalue as: (the scale factor*the phase+the first offset value)>>2,wherein the phase indicates a resampling filter phase in the firstdirection and the first offset value indicates a rounding offset.
 4. Theapparatus of claim 2, wherein the first direction is the horizontaldirection and the scale factor is based on a width of the referencelayer picture and a width of the enhancement layer picture.
 5. Theapparatus of claim 2, wherein the first direction is the horizontaldirection and the scale factor is based on a width of the referencelayer picture and a width of a scaled version of the reference layerpicture.
 6. The apparatus of claim 2, wherein the first direction is thevertical direction and the scale factor is based on a height of thereference layer picture and a height of the enhancement layer picture.7. The apparatus of claim 2, wherein the first direction is the verticaldirection and the scale factor is based on a height of the referencelayer picture and a height of a scaled version of the reference layerpicture.
 8. The apparatus of claim 5, wherein the scale factor in thehorizontal direction is determined as (1) a sum of (a) the width of thereference layer picture shifted left by 16 bits and (b) the width of thescaled version of the reference layer picture shifted right by 1 bit,divided by (2) the width of the scaled version of the reference layerpicture.
 9. The apparatus of claim 7, wherein the scale factor in thevertical direction is determined as (3) a sum of (c) the height of thereference layer picture shifted left by 16 bits and (d) the height ofthe scaled version of the reference layer picture shifted right by 1bit, divided by (4) the height of the scaled version of the referencelayer picture.
 10. The apparatus of claim 2, wherein the processor isfurther configured to determine the coordinate in the horizontaldirection of the first sample based at least in part on the coordinatein the horizontal direction of the second sample, wherein the coordinatein the horizontal direction of the first sample is relative to atop-left sample of the reference layer picture and the coordinate in thehorizontal direction of the second sample is relative to a top-leftsample of the enhancement layer picture.
 11. The apparatus of claim 2,wherein the processor is further configured to determine the coordinatein the vertical direction of the first sample based at least in part onthe coordinate in the vertical direction of the second sample, whereinthe coordinate in the vertical direction of the first sample is relativeto a top-left sample of the reference layer picture and the coordinatein the vertical direction of the second sample is relative to a top-leftsample of the enhancement layer picture.
 12. The apparatus of claim 10,wherein the coordinate in the horizontal direction of the first sampleis determined according to the equation:(((the coordinate in the horizontal direction of the second sample−afirst horizontal offset)*the scale factor in the horizontaldirection+the rounding offset value+(1 <<11))>>12)+(a horizontalphase<<2), wherein the horizontal phase indicates a resampling filterphase in the horizontal direction and the first horizontal offsetindicates a horizontal offset for a color coordinate between a top-leftsample of a resampled version of the reference layer picture and thetop-left sample of the enhancement layer picture.
 13. The apparatus ofclaim 11, wherein the coordinate in the vertical direction of the firstsample is determined according to the equation:(((the coordinate in the vertical direction of the second sample —afirst vertical offset)*the scale factor+the rounding offsetvalue+(1<<11))>>12)−(a vertical phase<<2), wherein the vertical phaseindicates a resampling filter phase in the vertical direction and thefirst vertical offset indicates a vertical offset for a color coordinatebetween a top-left sample of a resampled version of the reference layerpicture and the top-left sample of the enhancement layer picture. 14.The apparatus of claim 1, wherein the rounding offset value is used inposition calculation in a resampling process.
 15. The apparatus of claim1, wherein the processor is further configured to resample the firstsample by applying a resampling filter to the first sample.
 16. Theapparatus of claim 1, wherein the apparatus is selected from a groupconsisting of: a desktop computer, a notebook computer, a laptopcomputer, a tablet computer, a set-top box, a telephone handset, a smartphone, a smart pad, a television, a camera, a display device, a digitalmedia player, a video gaming console, and a video streaming device. 17.A method of coding video information, the method comprising: storingvideo data associated with a reference layer picture and an enhancementlayer picture; receiving a scale factor that indicates a proportion ofscaling between the reference layer picture and the enhancement layerpicture in a first direction; determining, based at least in part on thescale factor, a rounding offset value for determining a coordinate inthe first direction of a first sample in the reference layer picturebased at least in part on a coordinate in the first direction of asecond sample in the enhancement layer picture that corresponds to thefirst sample, the rounding offset value further determined in anoperation without a division operator, wherein the rounding offset valueis further determined as a sum that is bit-shifted by an integer value,the sum determined based on a summation of (i) a product of the scalefactor and a phase and (ii) a first offset value; determining thecoordinate in the first direction of the first sample using the scalefactor and the rounding offset value; and encoding, by a video encoder,or decoding, by a video decoder, the enhancement layer picture based onthe first sample at the determined coordinate.
 18. The method of claim17, wherein the first direction is a horizontal direction or a verticaldirection.
 19. The method of claim 17, wherein said determining therounding offset value comprises determining the rounding offset valueas: (the scale factor*the phase+the first offset value)>>2, wherein thephase indicates a resampling filter phase in the first direction and thefirst offset value indicates a rounding offset.
 20. The method of claim18, wherein the first direction is the horizontal direction and thescale factor is based on a width of the reference layer picture and awidth of the enhancement layer picture.
 21. The method of claim 18,wherein the first direction is the horizontal direction and the scalefactor is based on a width of the reference layer picture and a width ofa scaled version of the reference layer picture.
 22. The method of claim18, wherein the first direction is the vertical direction and the scalefactor is based on a height of the reference layer picture and a heightof the enhancement layer picture.
 23. The method of claim 18, whereinthe first direction is the vertical direction and the scale factor isbased on a height of the reference layer picture and a height of ascaled version of the reference layer picture.
 24. The method of claim21, wherein the scale factor in the horizontal direction is determinedas (1) a sum of (a) the width of the reference layer picture shiftedleft by 16 bits and (b) the width of the scaled version of the referencelayer picture shifted right by 1 bit, divided by (2) the width of thescaled version of the reference layer picture.
 25. The method of claim23, wherein the scale factor in the vertical direction is determined as(3) a sum of (c) the height of the reference layer picture shifted leftby 16 bits and (d) the height of the scaled version of the referencelayer picture shifted right by 1 bit, divided by (4) the height of thescaled version of the reference layer picture.
 26. A non-transitorycomputer readable medium comprising instructions that when executed on aprocessor comprising computer hardware cause the processor to: storevideo data associated with a reference layer picture and an enhancementlayer picture; receive a scale factor that indicates a proportion ofscaling between the reference layer picture and the enhancement layerpicture in a first direction; determine, based at least in part on thescale factor, a rounding offset value for determining a coordinate inthe first direction of a first sample in the reference layer picturebased at least in part on a coordinate in the first direction of asecond sample in the enhancement layer picture that corresponds to thefirst sample, the rounding offset value further determined in anoperation without a division operator, wherein the rounding offset valueis further determined as a sum that is bit-shifted by an integer value,the sum determined based on a summation of (i) a product of the scalefactor and a phase and (ii) a first offset value; determine thecoordinate in the first direction of the first sample using the scalefactor and the rounding offset value; and encode or decode theenhancement layer picture based on the first sample at the determinedcoordinate.
 27. The computer readable medium of claim 26, furthercomprising instructions to cause the processor to determine the roundingoffset value as: (the scale factor*the phase+the first offset value)>>2,wherein the phase indicates a resampling filter phase in the firstdirection and the first offset value indicates a rounding offset.
 28. Anapparatus for coding video information, the apparatus comprising: meansfor storing video data associated with a reference layer picture and anenhancement layer picture; means for receiving a scale factor thatindicates a proportion of scaling between the reference layer pictureand the enhancement layer picture in a first direction; means fordetermining, based at least in part on the scale factor, a roundingoffset value for determining a coordinate in the first direction of afirst sample in the reference layer picture based at least in part on acoordinate in the first direction of a second sample in the enhancementlayer picture that corresponds to the first sample, the rounding offsetvalue further determined in an operation without a division operator,wherein the rounding offset value is further determined as a sum that isbit-shifted by an integer value, the sum determined based on a summationof (i) a product of the scale factor and a phase and (ii) a first offsetvalue; means for determining the coordinate in the first direction ofthe first sample using the scale factor and the rounding offset value;and means for encoding or decoding the enhancement layer picture basedon the first sample at the determined coordinate.
 29. The apparatus ofclaim 28, wherein the means for determining the rounding offset value isfurther configured to determine the rounding offset value as: (the scalefactor*the phase+the first offset value)>>2, wherein the phase indicatesa resampling filter phase in the first direction and the first offsetvalue indicates a rounding offset.